I made one too using 1" Styrofoam and furring strips. Just four sides with a hinged top which can be raised by a rope (guided by pulleys) going through the ceiling of a clothes closet.
I made a cover out of 1x2 furring strips frame and covered the frame with 3/4-foam sheet insulation. It was four sides and a top. I made mine in panels to get it through the access whole then assembled the panels with sheetrock screws. When determining the height, make it tall enough to cover the housing, but not so tall that it cannot be removed by lifting it off. I also open the breaker to the fan when the cover is on during the winter so someone wouldn't turn the fan on with the cover in place.

Aaron George